In an imaging device using a solid-state image sensing device such as a CCD or a COMS image sensing device, which is mounted on a digital still camera and the like, an optical filter (near-infrared cut filter) that transmits visible light and blocks near-infrared light has been used for the purpose of well reproducing a color tone and obtaining a clear image. In such an optical filter, particularly a dye having high absorbency in a near-infrared region and having a high transmitting property in a visible region is used, thereby making it possible to obtain a steep cutoff property with respect to the near-infrared light and obtain good color reproducibility of an image by visible light.
In the meantime, even though the both properties of the high cutoff property of near-infrared light and the high transmitting property of visible light are tried to be obtained, it is difficult to obtain a 100% transmittance with respect to the light in the entire visible region, and a region relatively low in transmittance exists in the visible region. For example, an already-known squarylium-based dye is excellent in cutoff property of near-infrared light, has a high level of visible light transmittance, and has a characteristic in which the transmittance toward the near-infrared region from the visible region changes steeply. The present applicant has found out before that an optical filter containing the squarylium-based dye enables achievement of a visible light transmittance of a certain level or more (Patent Reference 1 (International Publication WO2014/088063)). However, a demand for higher precision color reproducibility is increasing by further increasing the visible light transmittance. Particularly, there is strongly growing a demand for increasing the precision of color reproducibility of a blue colored image by more increasing the transmittance of light with a wavelength of 430 to 550 nm being a relatively short wavelength in the visible region.
Thus, for the purpose of increasing the visible light transmittance, various squarylium dyes having a new structure also have been proposed, but have not reached a satisfactory level yet (Patent Reference 2 (JP-A 2014-148567) and Patent Reference 3 ((International Publication WO2011/086785)).
Further, there has been proposed an optical filter using a squarylium-based dye and a phthalocyanine-based dye in combination (Patent Reference 4 (International Publication WO2013/054864)), but as the transmitting property of visible light, the technique of increasing a transmittance with respect to light with a wavelength of 430 to 550 nm in particular has not been disclosed therein. Further, Patent Reference 4 uses a plurality of kinds of different dyes, and therefore visible light absorption increases collaterally, resulting in that there is also a problem of failing to obtain a high visible light transmittance.